Oct. 15, 2012 -- Getting the HPV vaccine is not linked to signs of increased
sexual activity in preteen girls, a new study shows.

Genital HPV, or human papillomavirus, is a sexually transmitted infection. Gardasil, an HPV vaccine approved in 2006, and Cervarix, a second HPV vaccine approved in 2009, target the two types of the virus that cause about 70% of cervical cancers. Gardasil also protects against two other types of HPV that cause about 90% of genital warts.

In 2006, the CDC's advisory committee on immunization practices recommended vaccinating all U.S. girls aged 11 and 12 -- before they became sexually active, so they'd develop immunity before being exposed to HPV.

But the committee's move raised concerns that vaccinating preteens against a sexually transmitted infection could lead to increased promiscuity, Kaiser Permanente researchers write in Pediatrics.

In previous studies of this question, teenage girls said they wouldn't change their sexual behavior after HPV vaccination, but scientists couldn't be sure they were being honest, according to the researchers who conducted the new study.

Getting to the Truth

To get around that problem, the scientists turned to Kaiser Permanente databases that contained information about doctor visits and laboratory tests. Researchers used data of almost 1,400 girls who had the opportunity to receive the HPV vaccine at age 11 or 12 during the period between July 2006 and December 2007. Of those girls, 493 were vaccinated against HPV.

Using data through 2010, the scientists compared the rates of testing or diagnosis of pregnancy or sexually transmitted infection and contraceptive counseling between the vaccinated and unvaccinated groups. They found little difference between them.

"I think the findings from this study were very reassuring, because they did fall right in line with those other self-reported studies," says researcher Robert Bednarczyk, PhD, clinical investigator at the Kaiser Permanente Center for Health Research Southeast in Atlanta, and an epidemiologist at Emory University.

The researchers have no plans to continue following the girls, because any impact on behavior would most likely be seen within a year and a half of immunization, Bednarczyk says. However, he says, similar studies should be done in older girls as well as in boys.

In October 2011, the CDC's immunization advisory committee began recommending that boys be immunized with the HPV vaccine Gardasil, which protects against genital warts and anal cancer.

Obstacles to Immunization

Although the number of girls getting the HPV vaccine has been rising, it's still not as high as that of other vaccines recommended for teens, Bednarczyk and his collaborators write.

Besides parents' worry that vaccinating their young daughters could lead to promiscuity, obstacles also include the fact that the vaccine is a three-shot series given over six months, there are concerns about its safety, and there is the fear of needles, the researchers say.

In a previous study, Bednarczyk says, he had surveyed college-aged women about the vaccine. About 1 in 10 of those who hadn't been immunized said their parents wouldn't let them get the vaccine, he says.

Earlier this month, another study, published online in the Archives of Pediatric & Adolescent Medicine, found no serious health problems linked to Gardasil in the 60 days after immunization.

The study focused on nearly 200,000 girls and young women who got their initial Gardasil shot during the vaccine's first 20 months on the market. Immunization was linked only with fainting on the day of the shot and skin infections in the two weeks afterward.

"There have been a number of safety studies, and all of them have been very consistent," says researcher Nicola Klein, MD, PhD, co-director of the Kaiser Permanente Vaccine Study Center in Oakland, Calif.

Fainting probably had more to do with getting a shot than with Gardasil in particular, Klein says. It's not clear whether the skin infections were due to the injection itself or to the vaccine, she says.

"I think these studies [Bednarczyk's and hers] in total are very reassuring," Klein says.